#include<stdio.h>
#include<math.h>
	int main(void)
	{  
	  /*********Begin*********/
	  double a, b, c, s, area;
      scanf("%lf%lf%lf", &a, &b, &c);
      s = (a + b + c) / 2;
      area = sqrt(s * (s - a) * (s - b) * (s - c));
      printf("%.3f", area);
	  /*********End**********/ 
       return 0;
	}
